Crypt::Eksblowfish::Family - Eksblowfish cipher family

	use Crypt::Eksblowfish::Family;

	$family = Crypt::Eksblowfish::Family->new_family(8, $salt);

	$cost = $family->cost;
	$salt = $family->salt;
	$block_size = $family->blocksize;
	$key_size = $family->keysize;
	$cipher = $family->new($key);

An object of this class represents an Eksblowfish cipher family. It contains the family parameters (cost and salt), and if combined with a key it yields an encryption function. See Crypt::Eksblowfish for discussion of the Eksblowfish algorithm.

It is intended that an object of this class can be used in situations such as the "-cipher" parameter to Crypt::CBC. Normally that parameter is the name of a class, such as "Crypt::Rijndael", where the class implements a block cipher algorithm. The class provides a new constructor that accepts a key. In the case of Eksblowfish, the key alone is not sufficient. An Eksblowfish family fills the role of block cipher algorithm. Therefore a family object is used in place of a class name, and it is the family object the provides the new constructor.

Crypt::CBC itself has a problem, with the result that this class can no longer be used with it in the manner originally intended.

When this class was originally designed, it worked with Crypt::CBC as described above: an object of this class would be accepted by Crypt::CBC as a cipher algorithm, and Crypt::CBC would happily supply it with a key and encrypt using the resulting cipher object. Crypt::CBC didn't realise it was dealing with a family object, however, and there was some risk that a future version might accidentally squash the object into a string, which would be no use. In the course of discussion about regularising the use of cipher family objects, the author of Crypt::CBC got hold of the wrong end of the stick, and ended up changing Crypt::CBC in a way that totally breaks this usage, rather than putting it on a secure footing.

The present behaviour of Crypt::CBC is that if an object (rather than a class name) is supplied as the "-cipher" parameter then it has a completely different meaning from usual. In this case, the object supplied is used as the keyed cipher, rather than as a cipher algorithm which must be given a key. This bypasses all of Crypt::CBC's usual keying logic, which can hash and salt a passphrase to generate the key. It is arguably a useful feature, but it's a gross abuse of the "-cipher" parameter and a severe impediment to the use of family-keyed cipher algorithms.

This class now provides a workaround. For the benefit of Crypt::CBC, and any other crypto plumbing that requires a keyable cipher algorithm to look like a Perl class (rather than an object), a family object of this class can in fact be reified as a class of its own. See the method as_class.

Crypt::Eksblowfish::Family->new_family(COST, SALT)

Creates and returns an object representing the Eksblowfish cipher family specified by the parameters. The SALT is a family key, and must be exactly 16 octets. COST is an integer parameter controlling the expense of keying: the number of operations in key setup is proportional to 2^COST.

$family->cost

Extracts and returns the cost parameter.

$family->salt

Extracts and returns the salt parameter.

$family->blocksize

Returns 8, indicating the Eksblowfish block size of 8 octets.

$family->keysize

Returns 0, indicating that the key size is variable. This situation is handled specially by Crypt::CBC.

$family->new(KEY)

Performs key setup on a new instance of the Eksblowfish algorithm, returning the keyed state. The KEY may be any length from 1 octet to 72 octets inclusive. The object returned is of class Crypt::Eksblowfish; see Crypt::Eksblowfish for the encryption and decryption methods.

Note that this method is called on a family object, not on the class Crypt::Eksblowfish::Family.

$family->encrypt

This method nominally exists, to satisfy Crypt::CBC. It can't really be used: it doesn't make any sense.

$family->as_class

Generates and returns (the name of) a Perl class that behaves as a keyable cipher algorithm identical to this Eksblowfish cipher family. The same methods that can be called as instance methods on $family can be called as class methods on the generated class.

You should prefer to use the family object directly wherever you can. Aside from being a silly indirection, the classes generated by this method cannot be garbage-collected. This method exists only to cater to Crypt::CBC, which requires a keyable cipher algorithm to look like a Perl class, and won't operate correctly on one that looks like an object.

Crypt::CBC, Crypt::Eksblowfish

Andrew Main (Zefram) <zefram@fysh.org>

Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Andrew Main (Zefram) <zefram@fysh.org>

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.